It is known to fabricate containers by blow molding, wherein a substantially tubular plastic parison commonly referred to as a “preform” is disposed in the cavity of a mold and expanded into the shape thereof by the injection of a pressurized fluid into said preform. This method lends itself well to the rapid fabrication of containers of consistently high quality.
A common variant of this process is stretch blow molding, in which a stretching rod is inserted into the preform and urged against an interior surface thereof, inducing the preform to deform along its longitudinal axis. This is particularly favored in that it enables one to exercise a greater deal of control over the longitudinal deformation of the preform, thereby enabling the production of a wider range of container shapes and sizes than by simple expansion alone.
A typical blow-molding apparatus comprises a mold, in which is provided a mold cavity in the form of the container to be produced. The preform is provided in a substantially tubular form globally resembling a test tube and which is disposed at least partially within the mold, conventionally being inserted into the mold cavity through a hole disposed in an upper surface of the mold.
Preferably, a small portion of the preform protrudes from the mold, permitting the attachment of an injection head to a mouth of the preform in communication with an internal cavity of the preform. This mouth portion of the preform is usually furnished with threads, rims, or other such means for interfacing with a closure device such as a cap, and remains substantially unchanged during the container forming process while the rest of the preform is expanded into a container. Generally, the preform is provided with a neck ring, which during the molding process sits upon the top surface of the mold and prevents the preform from falling through.
Optionally, the preform is heated prior to being inserted into the mold, to facilitate its deformation during the forming of the container.
The injection head is the means by which the molding apparatus interfaces with the preform, the injection head comprising a nozzle or other such channel configured to establish fluid communication between the mouth of the preform and a source of a pressurized fluid. During the operation of the apparatus, the pressurized fluid is injected into the cavity of the preform through the injection head, thereby inducing the preform to undergo plastic deformation and expand to assume the contours of the mold.
Since the fluid is injected at high pressure into the preform, it becomes necessary to provide a means in the nozzle of the injection head to create a secure seal with the preform, so as to avoid leakage of the pressurized fluid and subsequent malformations of the container due to the resultant loss of pressure.
Generally, this is accomplished by creating a seal between the nozzle and the top surface of the mold around the mouth of the preform. For example, the French patent application publication No 2 848 905 describes an injection head which is broadly bell-shaped, being configured to fit over the portion of the preform which protrudes from the mold. The injection head is pressed against the mold by mechanical, pneumatic, hydraulic, or magnetic means, creating a sealed chamber in communication with the cavity of the preform by way of the seal between its rim and the top surface of the mold surrounding the preform.
As initially conceived, the pressurized fluid injected into the preform is a gas, for instance compressed air. It has become known to inject a liquid into the preform, in particular the liquid which is ultimately to be packaged in the container thereby fabricated. This is advantageous relative to the former technique, in that it combines the steps for forming and filling the container and thereby realizes economies of space and time in the production of containers.
However, the injection nozzles known in the prior art are far from ideal for the injection of liquids. Specifically, the bell-shaped design of the nozzles known in the prior art, which seal to the top surface of the mold, will result in an amount of injection liquid being retained in the space above and around the preform within the injection nozzle.
This liquid will leak from the injection nozzle when the seal between it and the mold is broken, and infiltrate the mold cavity when the mold is opened to remove the finished container. The presence of the liquid within the mold cavity will cause malformations of the container in subsequent container forming cycles of the apparatus, hinder the attachment of labels or other markings to the container, and may implicate cleanliness concerns if the injection liquid contains alimentary substances such as oils or sugars. Such systems require the use of cleaning and/or drying systems to clean the mold cavity and the container after the conclusion of the forming process, adding expense to the forming process and slowing the rate at which containers may be formed and filled.
It is therefore an object of the invention to provide an injection nozzle for a blow molding apparatus which resolves the disadvantages of the prior art as detailed above.